The objectives of this research program are to elucidate the regulatory mechanisms of circadian variation in metabolic rate and body temperature during sleep and wakefulness in mammals and birds. Relations between daily changes and energy reserves and changes in circadian rhythms of metabolism and body temperature (Tb) in fasting pigeons will be investigated by continuous 24-hr measurement of metabolic rate (MR), while manipulating energy reserves through diurnal intravenous infusions of glucose. Our working hypothesis is that nocturnal metabolic rate (MR) is regulated at a level proportional to the diurnal energy reserves of the bird. Algebraic equations and parameters describing such relations between energy reserves and MR will be determined through statistical curve-fitting procedures. Simultaneous 24-hr recordings of electroencephalogram (EEG), electromyogram (EMG), ad electroculogram (EOG) will allow determination of whether changes in the durations and circadian distribution of stages of sleep are also related to changes in daily energy reserves. Relations between plasma glucose concentrations and R and Tb will be examined through assays of blood samples taken every 6 hr. These studies will establish a model for analysis of relations between energy metabolism during wakefulness and subsequent natural sleep that can then be applied in similar studies on mammalian species. There is evidence that humans also lower their metabolism in association with increased amounts of slow wave sleep (stages 3 and 4) when fasting. Therefore, these studies not only have relevance to the establishment of physiological homologies between sleep, circadian torpor and hibernation, but might also have clinical applications in the treatment of sleep disturbances and weight disorders.